Bone grafts

ABSTRACT

Spinal spacers  20  are provided for fusion of a motion segment. The spacers include a load bearing member  21  having a wall  22  sized for engagement within a space between adjacent vertebrae to maintain the space and an effective amount of an osteogenic composition to stimulate osteoinduction. The osteogenic composition includes a substantially pure osteogenic factor in a pharmaceutically acceptable carrier. In one embodiment the load bearing member includes a bone graft impregnated in an osteogenic composition. In another embodiment, the osteogenic composition  30  is packed within a chamber  25  defined in the graft. Any suitable configuration of a bone graft is contemplated, including bone dowels, D-shaped spacers and cortical rings.

FIELD OF THE INVENTION

[0001] The present invention relates to spacers, compositions,instruments and methods for arthrodesis. In specific applications of theinvention the spacers include bone grafts in synergistic combinationwith osteogenic compositions.

BACKGROUND OF THE INVENTION

[0002] Spinal fusion is indicated to provide stabilization of the spinalcolumn for painful spinal motion and disorders such as structuraldeformity, traumatic instability, degenerative instability, andpost-resection iatrogenic instability. Fusion, or arthrodesis, isachieved by the formation of an osseous bridge between adjacent motionsegments. This can be accomplished within the disc space, anteriorlybetween contiguous vertebral bodies or posteriorly between consecutivetransverse processes, laminae or other posterior aspects of thevertebrae.

[0003] An osseous bridge, or fusion mass, is biologically produced bythe body upon skeletal injury. This normal bone healing response is usedby surgeons to induce fusion across abnormal spinal segments byrecreating spinal injury conditions along the fusion site and thenallowing the bone to heal. A successful fusion requires the presence ofosteogenic or osteopotential cells, adequate blood supply, sufficientinflammatory response, and appropriate preparation of local bone. Thisbiological environment is typically provided in a surgical setting bydecortication, or removal of the outer, cortical bone to expose thevascular, cancellous bone, and the deposition of an adequate quantity ofhigh quality graft material.

[0004] A fusion or arthrodesis procedure is often performed to treat ananomoly involving an intervertebral disc. Intervertebral discs, locatedbetween the endplates of adjacent vertebrae, stabilize the spine,distribute forces between vertebrae and cushion vertebral bodies. Anormal intervertebral disc includes a semi-gelatinous component, thenucleus pulposus, which is surrounded and confined by an outer, fibrousring called the annulus fibrosis. In a healthy, undamaged spine, theannulus fibrosis prevents the nucleus pulposus from protruding outsidethe disc space.

[0005] Spinal discs may be displaced or damaged due to trauma, diseaseor aging. Disruption of the annulus fibrosis allows the nucleus pulposusto protrude into the vertebral canal, a condition commonly referred toas a herniated or ruptured disc. The extruded nucleus pulposus may presson the spinal nerve, which may result in nerve damage, pain, numbness,muscle weakness and paralysis. Intervertebral discs may also deterioratedue to the normal aging process or disease. As a disc dehydrates andhardens, the disc space height will be reduced leading to instability ofthe spine, decreased mobility and pain.

[0006] Sometimes the only relief from the symptoms of these conditionsis a discectomy, or surgical removal of a portion or all of anintervertebral disc followed by fusion of the adjacent vertebrae. Theremoval of the damaged or unhealthy disc will allow the disc space tocollapse. Collapse of the disc space can cause instability of the spine,abnormal joint mechanics, premature development of arthritis or nervedamage, in addition to severe pain. Pain relief via discectomy andarthrodesis requires preservation of the disc space and eventual fusionof the affected motion segments.

[0007] Bone grafts are often used to fill the intervertebral space toprevent disc space collapse and promote fusion of the adjacent vertebraeacross the disc space. In early techniques, bone material was simplydisposed between the adjacent vertebrae, typically at the posterioraspect of the vertebrae, and the spinal column was stabilized by way ofa plate or rod spanning the affected vertebrae. Once fusion occurred thehardware used to maintain the stability of the segment becamesuperfluous and was a permanent foreign body. Moreover, the surgicalprocedures necessary to implant a rod or plate to stabilize the levelduring fusion were frequently lengthy and involved.

[0008] It was therefore determined that a more optimal solution to thestabilization of an excised disc space is to fuse the vertebrae betweentheir respective end plates, preferably without the need for anterior orposterior plating. There have been an extensive number of attempts todevelop an acceptable intra-discal implant that could be used to replacea damaged disc and maintain the stability of the disc interspace betweenthe adjacent vertebrae, at least until complete arthrodesis is achieved.To be successful the implant must provide temporary support and allowbone ingrowth. Success of the discectomy and fusion procedure requiresthe development of a contiguous growth of bone to create a sclid massbecause the implant may not withstand the cyclic compressive spinalloads for the life of the patient.

[0009] Many attempts to restore the intervertebral disc space afterremoval of the disc have relied on metal devices. U.S. Pat. No.4,878,915 to Brantigan teaches a solid metal plug. U.S. Pat. Nos.5,044,104; 5,026,373 and 4,961,740 to Ray; U.S. Pat. No. 5,015,247 toMichelson and U.S. Pat. No. 4,820,305 to Harms et al., U.S. Pat. No.5,147,402 to Bohler et al. and U.S. Pat. No. 5,192,327 to Brantiganteach hollow metal cage structures. Unfortunately, due to the stiffnessof the material, some metal implants may stress shield the bone graft,increasing the time required for fusion or causing the bone graft toresorb inside the cage. Subsidence, or sinking of the device into bone,may also occur when metal implants are implanted between vertebrae iffusion is delayed. Metal devices are also foreign bodies which can neverbe fully incorporated into the fusion mass.

[0010] Various bone grafts and bone graft substitutes have also beenused to promote osteogenesis and to avoid the disadvantages of metalimplants. Autograft is often preferred because it is osteoinductive.Both allograft and autograft are biological materials which are replacedover time with the patient's own bone, via the process of creepingsubstitution. Over time a bone graft virtually disappears unlike a metalimplant which persists long after its useful life. Stress shielding isavoided because bone grafts have a similar modulus of elasticity as thesurrounding bone. Commonly used implant materials have stiffness valuesfar in excess of both cortical and cancellous bone. Titanium alloy has astiffness value of 114 Gpa and 316 L stainless steel has a stiffness of193 Gpa. Cortical bone, on the other hand, has a stiffness value ofabout 17 Gpa. Moreover, bone as an implant also allows excellentpostoperative imaging because it does not cause scattering like metallicimplants on CT or MRI imaging.

[0011] Various implants have been constructed from bone or graftsubstitute materials to fill the intervertebral space after the removalof the disc. For example, the Cloward dowel is a circular graft made bydrilling an allogenic or autogenic plug from the illium. Cloward dowelsare bicortical, having porous cancellous bone between two corticalsurfaces. Such dowels have relatively poor biomechanical properties, inparticular a low compressive strength. Therefore, the Cloward dowel isnot suitable as an intervertebral spacer without internal fixation dueto the risk of collapsing prior to fusion under the intense cyclic loadsof the spine.

[0012] Bone dowels having greater biomechanical properties have beenproduced and marketed by the University of Florida Tissue Bank, Inc., 1Progress Boulevard, P.O. Box 31, S. Wing, Alacllua, Fla. 32615.Unicortical dowels from allogenic femoral or tibial condyles areavailable. The University of Florida has also developed a diaphysialcortical dowel having superior mechanical properties. This dowel alsoprovides the further advantage of having a naturally preformed cavityformed by the existing meduallary canal of the donor long bone. Thecavity can be packed with osteogenic materials such as bone orbioceramic.

[0013] Unfortunately, the use of bone grafts presents severaldisadvantages. Autograft is available in only limited quantities. Theadditional surgery also increases the risk of infection and blood lossand may reduce structural integrity at the donor site. Furthermore, somepatients complain that the graft harvesting surgery causes moreshort-term and long-term pain than the fusion surgery.

[0014] Allograft material, which is obtained from donors of the samespecies, is more readily obtained. However, allogenic bone does not havethe osteoinductive potential of autogenous bone and therefore mayprovide only temporary support. The slow rate of fusion usingallografted bone can lead to collapse of the disc space before fusion isaccomplished.

[0015] Both allograft and autograft present additional difficulties.Graft alone may not provide the stability required to withstand spinalloads. Internal fixation can address this problem but presents its owndisadvantages such as the need for more complex surgery as well as thedisadvantages of metal fixation devices. Also, the surgeon is oftenrequired to repeatedly trim the graft material to obtain the correctsize to fill and stabilize the disc space. This trial and error approachincreases the length of time required for surgery. Furthermore, thegraft material usually has a smooth surface which does not provide agood friction fit between the adjacent vertebrae. Slippage of the graftmay cause neural and vascular injury, as well as collapse of the discspace. Even where slippage does not occur, micromotion at thegraft/fusion-site interface may disrupt the healing process that isrequired for fusion.

[0016] Several attempts have been made to develop a bone graftsubstitute which avoids the disadvantages of metal implants and bonegrafts while capturing advantages of both. For example Unilab, Inc.markets various spinal implants composed of hydroxyapatite and bovinecollagen. In each case developing an implant having the biomechanicalproperties of metal and the biological properties of bone without thedisadvantages of either has been extremely difficult or impossible.

[0017] A need has remained for fusion spacers which stimulate boneingrowth and avoid the disadvantages of metal implants yet providesufficient strength to support the vertebral column until the adjacentvertebrae are fused.

SUMMARY OF THE INVENTION

[0018] In accordance with one aspect of the invention, spinal spacersand compositions are provided for fusion of a motion segment. Thespacers include a load bearing member sized for engagement within aspace between adjacent vertebrae to maintain the space and an effectiveamount of an osteogenic composition to stimulate osteoinduction. Theosteogenic composition includes a substantially pure osteogenic factorin a pharmaceutically acceptable carrier. In one embodiment the loadbearing member includes a bone graft impregnated with an osteogeniccomposition. In another embodiment, the osteogenic composition is packedwithin a chamber defined in the graft. The grafts include bone dowels,D-shaped spacers and cortical rings.

[0019] One object of the invention is to provide spacers for engagementbetween vertebrae which encourages bone ingrowth and avoids stressshielding. Another object of the invention is to provide a spacer whichrestores the intervertebral disc space and supports the vertebral columnwhile promoting bone ingrowth.

[0020] One benefit of the spacers of the present invention is that theycombine the advantages of bone grafts with the advantages of metals,without the corresponding disadvantages. An additional benefit is thatthe invention provides a stable scaffold for bone ingrowth before fusionoccurs. Still another benefit of this invention is that it allows theuse of bone grafts without the need for metal cages or internalfixation, due to the increased speed of fusion. Other objects andfurther benefits of the present invention will become apparent topersons of ordinary skill in the art from the following writtendescription and accompanying Figures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 is a top perspective view of a bone dowel according to thisinvention.

[0022]FIG. 2 shows bilateral dowel placement between L5 and the sacrum.

[0023]FIG. 3 is a perspective view of a cortical dowel having a chamber.

[0024]FIG. 4 is a side perspective view of a dowel according to thisinvention.

[0025]FIG. 5 is a cross-section of another dowel of this invention.

[0026]FIG. 6 is a side elevational view of the dowel shown in FIG. 5.

[0027]FIG. 7 is a side elevational view of another dowel provided bythis invention.

[0028]FIG. 8 is a detail of the threads of the dowel shown in FIG. 7.

[0029]FIG. 9 is an insertion device for inserting the spacers of thisinvention.

[0030]FIG. 10A is a side perspective view of the dilation of a discspace.

[0031]FIG. 10B is a side elevational view of the dilation of a discspace.

[0032]FIG. 11A shows the seating of a single, barrel outer sleeve.

[0033]FIG. 11B is a side elevational view showing the outer sleeve inplace.

[0034]FIG. 12 shows the seating of a double barrel outer sleeve.

[0035]FIG. 13 shows the seating of the outer sleeve.

[0036]FIG. 14 shows the reaming of the disc space.

[0037]FIG. 15 depicts the reamer used in FIG. 14.

[0038]FIG. 16 shows the tapping of the disc space.

[0039]FIG. 17 shows the tap used in FIG. 16.

[0040]FIG. 18 shows an inserter engaged to a dowel.

[0041]FIG. 19 shows the inserter of FIG. 18 within a sleeve.

[0042]FIG. 20 depicts insertion of a dowel.

[0043]FIG. 21 is a side perspective view of a dural retractor.

[0044]FIG. 22 is a side elevational view of a guide protector.

[0045]FIG. 23 shows the insertion of the guide protector shown in FIG.22.

[0046]FIG. 24 is a partial cross-section of a spine showing bilateralplacement of two dowels.

[0047]FIG. 25 is a partial cross-section of a spine with a cortical ringimplanted.

[0048]FIG. 26 is a cortical ring packed with an osteogenic material.

[0049]FIG. 27 is yet another cortical ring embodiment provided by thisinvention.

[0050]FIG. 28 is another embodiment of a cortical ring provided by thisinvention.

[0051]FIG. 29 is a D-shaped spacer of this invention.

[0052]FIG. 30 is a front perspective view of the spacer of FIG. 29.

[0053]FIG. 31 is a front elevational view of the spacer depicted in FIG.29.

[0054]FIG. 32 is a top perspective view of the spacer of FIG. 29 showingthe chamber packed with a collagen sponge.

[0055]FIG. 33 is a top elevational view of a collagen sponge.

[0056]FIG. 34 is an implant insertion device.

[0057]FIG. 35 is a D-spaced spacer of this invention having a toolengaging hole.

[0058]FIG. 36 is a front elevational view of the spacer FIG. 35.

[0059]FIG. 37 depicts a side elevational view of an implanting tool.

[0060]FIG. 38 is top elevational view of another embodiment of thespacer.

[0061]FIG. 39 is a top elevational view of another embodiment of thespacer.

[0062]FIG. 40 is a top perspective view of another embodiment of thespacers of this invention having teeth.

[0063]FIG. 41 is a top elevational view of another embodiment of thespacer having blades.

[0064]FIG. 42 is a front elevational view of the spacer of FIG. 41.

[0065]FIG. 43 is a side elevational view of an autograft crock dowel.

[0066]FIG. 44 is a side elevational view of an autograft tricorticaldowel.

[0067]FIG. 45 is a side elevational view of an autograft button dowel.

[0068]FIG. 46 is a side elevational view of a hybrid autograftbutton/allograft crock dowel.

[0069]FIG. 47 is a perspective view of a threaded cortical threadeddiaphysial dowel having an osteogenic composition packed in the chamber.

[0070]FIG. 48 is a side perspective view of a dowel with an osteogeniccomposition packed within the chamber.

[0071]FIG. 49 is a side perspective view of a dowel with a ceramiccarrier packed within the chamber.

[0072]FIG. 50 is a side perspective view of an axial test fixture fortesting dowels of this invention.

[0073]FIG. 51 is a front cross-sectional view of the fixture of FIG. 50.

[0074]FIG. 52 is a side cross-sectional view of the fixture of FIGS. 50and 51.

[0075]FIG. 53 compares the compressive strength of a threaded corticaldowel to in vivo spinal loads.

[0076]FIG. 54 compares the compressive strength of the load bearingmembers of this invention to other known graft materials.

[0077]FIG. 55 compares the compressive strength of the a load bearingmember of this invention to fusion cages.

[0078]FIG. 56 compares the fatigue loading values for various spinalimplants in axial compression.

[0079]FIG. 57 is a side elevational view of a multi-axial loading testfixture.

[0080]FIG. 58 is a front elevational view of the fixture shown in FIG.57.

[0081]FIG. 59 compares insertion torque values for threaded corticaldowels and other threaded fusion spacers.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0082] For the purposes of promoting an understanding of the principlesof the invention, reference will now be made to the embodimentsillustrated in the drawings and specific language will be used todescribe the same. It will nevertheless be understood that no limitationof the scope of the invention is thereby intended, such alterations andfurther modifications in the illustrated spacers, and such furtherapplications of the principles of the invention as illustrated thereinbeing contemplated as would normally occur to one skilled in the art towhich the invention relates.

[0083] The present invention provides bone grafts in synergisticcombination with an osteogenic material, such as a bone morphogenicprotein (BMP). The combination of BMP with a bone graft provides theadvantages of a bone graft while enhancing bone growth into andincorporation of the graft, resulting in fusion quicker than with graftalone. The quicker fusion rates provided by this invention compensatefor the less desirable biomechanical properties of graft and makes theuse of internal fixation and metal interbody fusion devices unnecessary.The spacers of this invention are not required to support the cyclicloads of the spine for very long because of the quick fusion rates whichreduce the biomechanical demands on the spacer. Therefore this inventioncapitalizes on the advantages of graft while avoiding the disadvantages.

[0084] The spinal spacers of this invention include a load bearingmember sized for engagement within a space between adjacent vertebrae tomaintain the space. The load bearing member is a bone graft insynergistic combination with an osteogenic material. The bone graft isany suitable bone material, preferably of human origin, includingtibial, fibial, humeral, iliac, etc. The load bearing members of thisinvention include flat D-shaped spacers, bone dowels, cortical rings andany suitably shaped load bearing member composed of bone. A preferredload bearing member is obtained from the diaphysis of a long bone havinga medullary canal which forms a natural chamber in the graft.

[0085] This invention provides the further advantage of exploiting thediscovery that bone is an excellent carrier for osteogenic factors suchas bone morphogenic proteins. Hydroxyapatite which is very similar inchemical composition to the mineral in cortical bone is an osteogenicfactor-binding agent which controls the rate of delivery of certainproteins to the fusion site. Calcium phosphate compositions such ashydroxyapatite are thought to bind bone morphogenic proteins and preventBMP from prematurely dissipating from the spacer before fusion canoccur. It is further believed that retention of the BMP by the agentpermits the protein to initiate the transformation of mesenchymal stemcells into bone producing cells (osteoblasts) within the device at arate that is conducive to complete and rapid bone formation andultimately, fusion across the disc space. The spacers of this inventionhave the advantage of including a load bearing member composed of bonewhich naturally binds and provides controlled delivery of osteogenicfactors such as bone morphogenic proteins.

[0086] This invention also capitalizes on the discovery that corticalbone, like metal, can be conveniently machined into the various shapesdisclosed herein. In some embodiments, the load bearing members definethreads on an outer surface. Machined surfaces, such as threads, provideseveral advantages that were previously only available with metalimplants. Threads allow better control of spacer insertion than can beobtained with a smooth surface. This allows the surgeon to moreaccurately position the spacer which is extremely important around thecritical neurological and vascular structures of the spinal column.Threads and the like also provide increased surface area whichfacilitates the process of bone healing and creeping substitution forreplacement of the donor bone material and fusion. These features alsoincrease post-operative stability of the spacer by engaging the adjacentvertebral endplates and anchoring the spacer to prevent expulsion. Thisis a major advantage over smooth grafts. Surface features also stabilizethe bone-spacer interface and reduce micromotion to facilitateincorporation and fusion.

[0087] In one specific embodiment depicted in FIG. 1, the load bearingmember of the spacer 10 is a bone dowel 11 soaked with an effectiveamount of an osteogenic composition to stimulate osteoinduction.Preferably, the osteogenic composition includes a substantially pureosteogenic factor in a pharmaceutically acceptable carrier. The dowel 10includes a wall 12 sized for engagement within the intervertebral spaceIVS to maintain the space IVS. The wall 12 defines an outer engagingsurface 13 for contacting the adjacent vertebrae. The wall 12 ispreferably cylindrically so that the bone dowel 10 has a diameter dwhich is larger than the height h of the space IVS between adjacentvertebrae V or the height of the space between the lowest lumbarvertebrae L5 and the sacrum S as depicted in FIG. 2.

[0088] In another embodiment 20 depicted in FIG. 3, the load bearingmember is a bone dowel 21 which includes a wall 22 having an engagementsurface 23. The wall 22 defines a chamber 25 therethrough. Preferably,the load bearing member is a bone graft obtained from the diaphysis of along bone having a medullary canal which forms the chamber 25. Thechamber 25 is most preferably packed with an osteogenic composition tostimulate osteoinduction. The chamber 25 is preferably defined through apair of outer engaging surfaces 23 so that the composition has maximumcontact with the endplates of the adjacent vertebrae. Referring now toFIG. 4, the spacer 21 includes a solid protective wall 26 which ispositionable to protect the spinal cord from escape or leakage of theosteogenic composition 30 within the chamber 25. In anterior approaches,the protective wall 26 is posterior. Preferably, the osteogeniccomposition 30 has a length which is greater than the length of thechamber (FIGS. 5 and 6) and the composition 30 is disposed within thechamber 25 to contact the end plates of adjacent vertebrae when thespacer 20′ is implanted between the vertebrae. This provides bettercontact of the composition with the end plates to stimulateosteoinduction.

[0089] Various features can be machined on the outer surfaces of thedowels of this invention. In one embodiment shown in FIG. 7, the dowel40 includes an outer engaging surface 41 defining threads 42. Theinitial or starter thread 47 is adjacent the protective wall 26′. Asshown more clearly in FIG. 8, the threads are preferably uniformallymachined threads which include teeth 43 having a crest 44 between aleading flank 45 and an opposite trailing flank 46. Preferably the crest44 of each tooth 43 is flat. In one specific embodiment, the crest 44 ofeach tooth 43 has a width w of between about 0.020 inches and about0.030 inches. The threads 42 preferably define an angle α between theleading flank 45 and the trailing flank 46 of adjacent ones of saidteeth 43. The angle α is preferably between about 50 degrees and 70degrees. Each tooth 43 preferably has a height h′ which is about 0.030inches and about 0.045 inches.

[0090] Referring again to FIG. 7, in some embodiments, the dowel 40 isprovided with a tool engaging hole 49 in a wall 48 opposite the solidprotective wall 26′. The tool engaging hole 49 is provided in a surfaceof the dowel which is adjacent the surgeon and opposite the initialthread 47. For an anterior procedure, the tool engaging tool hole 49would be provided in the anterior surface 48 of the dowel 40. Othermachined features are contemplated in the outer or bone engagingsurfaces 41. Such machine features include surface roughenings such asknurlings and ratchetings.

[0091] In a most preferred embodiment, the tool engaging hole 49 isthreaded to receive a threaded tip of an implanting tool. The inserter60 shown in FIG. 9 includes a handle portion 61 and a shaft 62 extendsfrom the handle 61. The distal end 63 of the shaft 62 includes a tip 65which mates with the tool engaging hole 49. Preferably the tip 65 andthe tool engaging hole 49 have corresponding mating threads 66, 49A. Theinserter 60 preferably includes a T-handle for spacer control andpositioning. The shaft 62 of the inserter 60 also includes a depth stop64. Preferably the inserter 60 includes means for rotating the threadedtip 65. Knob 68 is engaged to the tip 65 through an intershaft extendingthrough an internal bore (not shown) in the handle 61 and in the shaft62. The tip 65 is preferably at the end of the intershaft with theintershaft rotatingly mounted within the handle 61 and the shaft 62.

[0092] The spacers of this invention can be inserted using conventionaltechniques. In accordance with additional aspects of the presentinvention, methods for implanting an interbody fusion spacer, such asthe spacer 40, are contemplated. These methods are also disclosed incommonly assigned, co-pending U.S. patent application Ser. No.08/604,874, METHODS AND INSTRUMENTS FOR INTERBODY FUSION. As apreliminary step, it is necessary to locate appropriate starting pointsfor implanting the fusion spacer, preferably bilaterally. In the firststep of an anterior approach, a distractor 75 is disposed between thevertebral end plates E to dilate the L4-L5 or L5-S1 disc space (FIGS.10A and 10B). (It is understood, of course, that this procedure can beapplied at other vertebral levels). In the second step, shown in FIG.11A, an outer sleeve 76 is disposed about the disc space IVS. The outersleeve 76 can be configured to positively engage the anterior aspect ofthe vertebral bodies to firmly, but temporarily, anchor the outer sleeve76 in position. In essence, this outer sleeve 76 operates as a workingchannel for this approach. In a preferred embodiment, a single barrelouter sleeve 76 a is first inserted (FIG. 11B) followed by a doublebarrel outer sleeve 76 b, (FIG. 12), finally followed by the outersleeve 76 (FIG. 13). One purpose of this tripartite sleeve system is toprovide an enlarged working channel for preparing the vertebrae andimplanting the fusion spacer. In the step shown in FIG. 14, a drill orreamer 77 (FIG. 15) is extended through the outer sleeve 76 and used todrill out circular openings in the adjacent vertebral bodies. Theopenings can be tapped (FIG. 16) with a tap 78 (FIG. 17) to facilitatescrew insertion of the fusion spacer 10, although this step is notnecessary.

[0093] The fusion spacer 40 is then engaged by an implant driver 60, 60′(FIGS. 18 & 19) and extended through the outer sleeve 76 as shown inFIG. 13. The spacer is then inserted into the disc space IVS until theinitial thread 47 contacts the bone opening as shown in FIG. 20. Theimplant driver 60 can then be used to screw thread the fusion spacerinto the tapped or untapped opening formed in the vertebral and endplate E. Once the dowel 40 is properly positioned, the knob 68 of thetool 60 can be turned to rotate the threaded tip 65 and disengage thetip 65 from the hole 49 of the dowel 40. The inserter 60 and the sleeve76 can be withdrawn from the surgical site leaving the dowel 40 inplace. It is understood that in this step, other suitable driving toolscould be used. It can been seen that once implanted, the closedposterior end 26 is directed toward the posterior aspect of thevertebrae. The chamber 25 packed with an osteogenic material ispositioned so that the osteogenic material contacts the end plates.

[0094] The spacers of this invention may also be used with posteriorapproaches. The steps of the posterior approach are similar to those ofthe prior anterior approach except that the tools are introducedposteriorly at the instrumented motion segment. This approach mayrequire decortication and removal of vertebral bone to accept the outersleeve 76. A dural retractor 80 as shown in FIG. 21 may be used toretract and protect the spinal cord and accessory tissues. The retractor80 includes a handle 81 which preferably includes a bend 82 tofacilitate manipulation of the tool. The dural retractor 80 has an end83 which is attached to the handle portion 81. The end 83 preferablyincludes a curve 84 which is configured to safely cradle the spinalcord.

[0095] With the spinal cord safely retracted, a seat guide protector 85(FIG. 22) can be pounded into position as shown in FIG. 23. The seatguide protector 85 can be similar to the sleeve 76 described above.Various tools, such as extractors, reamers and taps can be insertedthrough the seat guide protector similar as described above. The fusionspacer 40 can be inserted through the protector 85 into the dilated discspace.

[0096] With either the anterior or posterior approaches, the position ofthe fusion spacer 40 with respect to the adjacent vertebrae can beverified by radiograph or other suitable techniques for establishing theangular relationship between the vertebrae. Alternatively, the preferreddepth of insertion of the spacer can be determined in advance andmeasured from outside the patient as the spacer is positioned betweenthe vertebrae. The depth of insertion of the fusion spacer can beascertained using depth markings (not shown) on the implant driver 60.

[0097] The spacers of this invention can also be inserted usinglaproscopic technology as described in Sofamor Danek USA's LaproscovicBone Dowel Surgical Technique, © 1995, 1800 Pyramid Place, Memphis,Tenn. 38132, 1-800-933-2635. Devices of this invention can beconveniently incorporated into Sofamor Danek's laproscopic bone dowelsystem that facilitates anterior interbody fusions with an approach thatis much less surgical morbid than the standard open anteriorretroperitoneal approaches. This system includes templates, trephines,dilators, reamers, ports and other devices required for laproscopicdowel insertion.

[0098] Bilateral placement of dowels 40 is preferred as shown in FIGS. 2and 24. This configuration provides a substantial quantity of bone graftavailable for the fusion. The dual bilateral cortical dowels 40 resultin a significant area of cortical bone for load bearing and long-termincorporation via creeping substitution, while giving substantial areafor placement of osteogenic autogenous bone and boney bridging acrossthe disc space. Comparing FIG. 24 to FIG. 25, it can be seen thatbilateral placement of dowels 40 provides a greater surface area of bonematerial than a single ring allograft 50 which provides only a singlechamber 55 for packing with osteogenic material 30. The dual dowelplacement results in two chambers 25 that can be filled with anosteogenic composition. Additionally, osteogenic material 30 such ascancellous bone or BMP in a biodegradable carrier may be packed aroundthe dowels. This provides for the placement of a significant amount ofosteogenic material as well as four columns 35, 36, 37, 38 of corticalbone for load bearing.

[0099] The load bearing member may also include other grafts such ascortical rings as shown in FIG. 26. Such cortical rings 50 are obtainedby a cross-sectional slice of the diaphysis of a long bone and includesuperior surface 51 and inferior surface 52. The graft shown in FIG. 26includes an outer surface 53 which is adjacent and between the superior51 and inferior 52 surfaces. In one embodiment bone growth thru-holes 53a are defined through the outer surface 53 to facilitate fusion. Theholes 53 a allows mesenchymal stem cells to creep in and BMP protein todiffuse out of the graft. This facilitates bone graft incorporation andpossibly accelerates fusion by forming anterior and lateral bonebridging outside and through the device. In another embodiment the outersurface 53 defines a tool engaging hole 54 for receiving an implantingtool. In a preferred embodiment, at least one of the superior and/orinferior surfaces 51, 52 are roughened for gripping the end plates ofthe adjacent vertebrae. The surface roughenings may include teeth 56 onring 50′ as shown in FIG. 27 or waffle pattern 57 as shown on ring 50″in FIG. 28. When cortical rings are used as the graft material the ring50 may be trimmed for a more uniform geometry as shown in FIG. 26 orleft in place as shown in FIG. 28.

[0100] In another specific embodiment, spacers are provided forengagement between vertebrae as depicted in FIGS. 29-31. Spacers of thisinvention can be conveniently incorporated into current surgicalprocedures such as, the Smith-Robinson technique for cervical fusion(Smith, M. D., G. W. and R. A. Robinson, M. D., “The Treatment ofCertain Cervical-Spine Disorders By Anterior Removal Of TheIntervertebral Disc And Interbody Fusion”, J. Bone And Joint Surgery,40-A:607-624 (1958) and Cloward, M. D., R. B., “The Anterior ApproachFor Removal Of Ruptured Cervical Dislks”, in meeting of the HarveyCushing Society, Washington, D.C., Apr. 22, 1958). In such procedures,the surgeon prepares the endplates of the adjacent vertebral bodies toaccept a graft after the disc has been removed. The endplates aregenerally prepared to be parallel surfaces with a high speed burr. Thesurgeon then typically sculpts the graft to fit tightly between the bonesurfaces so that the graft is held by compression between the vertebralbodies. The bone graft is intended to provide structural support andpromote bone ingrowth to achieve a solid fusion of the affected joint.The spacers of this invention avoid the need for this graft sculpting asspacers of known size and dimensions are provided. This invention alsoavoids the need for a donor surgery because the osteoinductiveproperties of autograft are not required. The spacers can be combinedwith osteoinductive materials that make allograft osteoinductive.Therefore, the spacers of this invention speed the patient's recovery byreducing surgical time, avoiding a painful donor surgery and inducingquicker fusion.

[0101] The spacer 110 includes an anterior wall 111 having opposite ends112, 113, a posterior wall 115 having opposite ends 116, 117 and twolateral walls 120, 121. Each of the lateral walls 120, 121 is connectedbetween the opposite ends 112, 113, 116, 117 of the anterior 111 andposterior 115 walls to define a chamber 130. The walls are each composedof bone and also include the superior face 135 which defines a firstopening 136 in communication with the chamber 130. The superior face 135includes a first friction or vertebral engaging surface 137. As shown inFIG. 31, the walls further include an opposite inferior face 138defining a second opening 139 which is in communication with the chamber130. The chamber 130 is preferably sized to receive an osteogeniccomposition to facilitate bone growth. The inferior face 138 includes asecond friction or second vertebral engaging surface (not shown) whichis similar to or identical to the first friction or vertebral engagingsurface 137.

[0102] In one specific embodiment for an intervertebral disc replacementspacer, a hollow D-shaped spinal spacer is provided. The anterior wall111 as shown in FIGS. 29-31 is convexly curved. This anterior curvatureis preferred to conform to the geometry of the adjacent vertebral boneand specifically to the harder cortical bone of the vertebrae. TheD-shape of the spacer 110 also prevents projection of the anterior wall111 outside the anterior aspect of the disc space, which can beparticularly important for spacers implanted in the cervical spine.

[0103] In one specific embodiment shown in FIGS. 32 and 33, the D-shapedspacer 110 includes a collagen sponge 148 having a width w and length lwhich are each slightly greater than the width W and length L of thechamber. In a preferred embodiment, the sponge 148 is soaked with freezedried rhBMP-2 reconstituted in buffered physiological saline and thencompressed into the chamber 130. The sponge 148 is held within thechamber 130 by the compressive forces provided by the sponge 148 againstthe walls 111, 115, 120, 121 of the spacer 110.

[0104] The spacers are shaped advantageously for cervical arthrodesis.The flat posterior and lateral walls 115, 120 and 121, as shown in FIG.29, can be easily incorporated into Smith Robinson surgical fusiontechnique. After partial or total discectomy and distraction of thevertebral space, the surgeon prepares the end plates for the spacer 110preferably to create flat posterior and lateral edges. The spacer 110fits snugly with its flat surfaces against the posterior and lateraledges which prevents medial and lateral motion of the spacer 110 intovertebral arteries and nerves. This also advantageously reduces the timerequired for the surgery by eliminating the trial and error approach toachieving a good fit with bone grafts because the spacers can beprovided in predetermined sizes.

[0105] Devices such as the spacer 110 or dowel 40, which are notprovided with an insertion tool hole, can be inserted into the fusionsite during an open or percutaneous surgery using an insertion devicesuch as the one depicted in FIG. 34. The inserter 150 includes a handle151 with knurlings or other suitable patterns to enhance manual grippingof the handle. A shaft 152 extends from the handle 151 and is generallydivided into two portions: a solid portion 153 and a split jaw portion154. The split jaw portion 154 is at the distal end of the shaft 152opposite the handle 151. In the preferred embodiment, the split jawportion 154 includes two jaws 156 each having an offset gripping surface158 at their free ends. As depicted in FIG. 34 the split jaw portions154 are movable from a fully opened position as represented by the fullyseparated position of the gripping surfaces 158. The split jaw portion154 is closeable to a fully closed position in which the two jaws 156are in contact with one another. In the fully closed position, thegripping surfaces, identified as 158′ in FIG. 34, are separated by adistance sufficiently close to grip a hollow spacer 110 therebetween. Inparticular, the closed gripping surfaces 158′ contact the side surfacesof the two lateral walls 120, 121 of the spacer 110. In one preferredembodiment, the gripping surfaces 158 are roughened or knurled toenhance the grip on the spacer 110.

[0106] The inserter 150 further includes a sleeve 160 that isconcentrically disposed around shaft 152. Preferably the sleeve 160defines an inner bore 161 with a first portion 162 having a diameterslightly greater than the diameter of shaft 152. The internal bore 161includes a flared portion 163 at its distal end 164. In the preferredembodiment, when the jaws 156 of the split jaw portion 154 are in theirfully opened position, the jaws contact the flared portion 63 of thebore 161.

[0107] In the use of the inserter 150, the sleeve 160 is slid along theshaft 152, and more particularly along the opened jaws 156, to push thejaws together. As the jaws are pushed together, the gripping surfaces158 engage and firmly grip a spacer 110 as described above. Thisinserter can then be extended percutaneously into the surgical site toimplant a spacer 110 in the intra-discal space. Once the spacer isproperly positioned, the sleeve 160 can be moved back toward the handle151, so that the natural resilience of the two jaws 156 cause them tospread apart, thereby releasing the spacer 110. The inserter 150 canthen be withdrawn from the surgical site with the jaws fully opened, orthe sleeve can be advanced along the shaft once the gripping surfaces158 have cleared the spacer 110. Other details of a similar device aredisclosed in commonly assigned, pending U.S. application Ser. No.08/697,784, IMPLANT INSERTION DEVICE. Metal spacers, insertion devicesand methods relating to the same are disclosed in commonly assigned andco-pending applications: U.S. patent application Ser. No. 08/603,675,VERTEBRAL SPACER and U.S. patent application Ser. No. 08/603,676,INTERVERTEBRAL SPACER.

[0108] Alternatively, the spacers of this invention may be provided witha tool engaging hole for insertion such as the tool depicted in FIG. 9.According to another specific embodiment depicted in FIGS. 35 and 36,the spacer 170 includes an anterior wall 171 defining a tool engaginghole 174. In a most preferred embodiment, the tool engaging hole 174 isthreaded for receiving a threaded implanting tool such as depicted inFIG. 37. The inserter 220 includes a handle portion 221 with knurlingsor other suitable patterns to enhance manual gripping of the handle. Ashaft 222 extends from the handle 221. The distal end 223 of the shaft222 includes a tip 225 which mates with the tool engaging hole 174.Preferably the tip 225 and tool engaging hole 174 have correspondingmating threads 226, 178. Where the tool engaging hole 174 is defined ina curved wall as shown in FIG. 35, the distal end 223 of the shaft 222preferably includes a curved portion 224 that conforms to the curvedanterior surface of the spacer. The inserter 220 also preferablyincludes a T-handle 228 for spacer control and positioning. Preferablythe inserter 120 includes means for rotating the threaded tip 225. InFIG. 37, the knob 230 is engaged to the tip 225 via an inner shaftextending through an internal bore (not shown) in the handle 221 andshaft 222. The tip 225 is preferably at the end of the inner shaft withthe inner shaft rotatingly mounted within the handle 221 and shaft 222.

[0109] In the use of the inserter 220, a spacer 170 is engaged to thethreaded tip 225 with the curved portion 224 flush with the anteriorwall 171. The inserter and spacer can then be extended percutaneouslyinto the surgical site to implant the spacer in the intra-discal space.Once the spacer 170 is properly positioned, the knob 230 can be turnedto rotate the threaded tip 225 and disengage the tip from the hole 174of the spacer 110. The inserter 220 can then be withdrawn from thesurgical site leaving the spacer 170 in place.

[0110] In preferred embodiments, the engaging surfaces of the spacersare machined to facilitate engagement with the endplates of thevertebrae and prevent slippage of the spacer as is sometimes seen withsmooth graft prepared at the time of surgery. The spacer 180 may beprovided with a roughened surface 181 on one of the engaging surfaces187 of one or both of the superior face 185 or inferior face (not shown)as shown in FIG. 38. The roughened surface 191 of the spacer 190 mayinclude a waffle or other suitable pattern as depicted in FIG. 39. Inone preferred embodiment shown in FIG. 40, the engaging surfaces 201include teeth 205 which provide biting engagement with the endplates ofthe vertebrae. In another embodiment (FIGS. 41 and 42), the spacer 210includes engaging surfaces 211 machined to include one or more blades212. Each blade includes a cutting edge 213 configured to pierce avertebral end-plate. The blade 212 can be driven into the bone surfaceto increase the initial stability of the spacer.

[0111] Any suitable load bearing member which can be synergisticallycombined with an osteogenic composition is contemplated. Other potentialload bearing members include allograft crock dowels (FIG. 43),tricortical dowels (FIG. 44), button dowels (FIG. 45) and hybridallograft button-allograft crock dowels (FIG. 46).

[0112] An osteogenic material can be applied to the spacers of thisinvention by packing the chamber 25, 130 with an osteogenic material 30,148 as shown in FIGS. 32 and 47, by impregnating the graft with asolution including an osteogenic composition or by both methodscombined. The composition may be applied by the surgeon during surgeryor the spacer may be supplied with the composition preapplied. In suchcases, the osteogenic composition may be stabilized for transport andstorage such as by freeze-drying. The stablized composition can berehydrated and/or reactivated with a sterile fluid such as saline orwater or with body fluids applied before or after implantation. Anysuitable osteogenic material or composition is contemplated, includingautograft, allograft, xenograft, demineralized bone, synthetic andnatural bone graft substitutes, such as bioceramics and polymers, andosteoinductive factors. The term osteogenic composition used here meansvirtually any material that promotes bone growth or healing includingnatural, synthetic and recombinant proteins, hormones and the like.

[0113] Autograft can be harvested from locations such as the iliac crestusing drills, gouges, curettes and trephines and other tools and methodswhich are well known to surgeons in this field. Preferably, autograft isharvested from the iliac crest with a minimally invasive donor surgery.The graft may include osteocytes or other bone reamed away by thesurgeon while preparing the end plates for the spacer.

[0114] Advantageously, where autograft is chosen as the osteogenicmaterial, only a very small amount of bone material is needed to packthe chamber 130. The autograft itself is not required to providestructural support as this is provided by the spacer 110. The donorsurgery for such a small amount of bone is less invasive and bettertolerated by the patient. There is usually little need for muscledissection in obtaining such small amounts of bone. The presentinvention therefore eliminates many of the disadvantages of autograft.

[0115] The osteogenic compositions used in this invention preferablycomprise a therapeutically effective amount of a substantially pure boneinductive factor such as a bone morphogenetic protein in apharmaceutically acceptable carrier. The preferred osteoinductivefactors are the recombinant human bone morphogenic proteins (rhBMPs)because they are available in unlimited supply and do not transmitinfectious diseases. Most preferably, the bone morphogenetic protein isa rhBMP-2, rhBMP-4 or heterodimers thereof. The concentration of rhBMP-2is generally between about 0.4 mg/ml to about 1.5 mg/ml, preferably near1.5 mg/ml. However, any bone morphogenetic protein is contemplatedincluding bone morphogenetic proteins designated as BMP-1 throughBMP-13. BMPs are available from Genetics Institute, Inc., Cambridge,Mass. and may also be prepared by one skilled in the art as described inU.S. Pat. Nos. 5,187,076 to Wozney et al.; U.S. Pat. No. 5,366,875 toWozney et al.; U.S. Pat. No. 4,877,864 to Wang et al.; U.S. Pat. No.5,108,922 to Wang et al.; U.S. Pat. No. 5,116,738 to Wang et al.; U.S.Pat. No. 5,013,649 to Wang et al.; U.S. Pat. No. 5,106,748 to Wozney etal.; and PCT Patent Nos. WO93/00432 to Wozney et al.; WO94/26893 toCeleste et al.; and WO94/26892 to Celeste et al. All osteoinductivefactors are contemplated whether obtained as above or isolated frombone. Methods for isolating bone morphogenic protein from bone aredescribed in U.S. Pat. No. 4,294,753 to Urist and Urist et al., 81 PNAS371, 1984.

[0116] The choice of carrier material for the osteogenic composition isbased on biocompatibility, biodegradability, mechanical properties andinterface properties as well as the structure of the load bearingmember. The particular application of the compositions of the inventionwill define the appropriate formulation. Potential carriers includecalcium sulphates, polylactic acids, polyanhydrides, collagen, calciumphosphates, polymeric acrylic esters and demineralized bone. The carriermay be any suitable carrier capable of delivering the proteins. Mostpreferably, the carrier is capable of being eventually resorbed into thebody. One preferred carrier is an absorbable collagen sponge marketed byIntegra LifeSciences Corporation under the trade name Helistat®Absorbable Collagen Hemostatic Agent. Another preferred carrier is anopen cell polylactic acid polymer (OPLA). Other potential matrices forthe compositions may be biodegradable and chemically defined calciumsulfates, calcium phosphates such as tricalcium phosphate (TCP) andhydroxyapatite (HA) and including injectable bicalcium phosphates (BCP),and polyanhydrides. Other potential materials are biodegradable andbiologically derived, such as bone or dermal collagen. Further matricesare comprised of pure proteins or extracellular matrix components. Theosteoinductive material may also be an admixture of BMP and a polymericacrylic ester carrier, such as polymethylmethacrylic.

[0117] For packing the chambers of the spacers of the present invention,the carriers are preferably provided as a sponge 58, 30 which can becompressed into the chamber 55 (FIG. 25) or 25 (FIG. 47) or as strips orsheets which may be folded to conform to the chamber as shown in FIG.48. Preferably, the carrier has a width and length which are eachslightly greater than the width and length of the chamber. In the mostpreferred embodiments, the carrier is soaked with a rhBMP-2 solution andthen compressed into the chamber. As shown in FIG. 47, the sponge 30 isheld within the chamber 25 by the compressive forces provided by thesponge 30 against the wall 22 of the dowel 21. It may be preferable forthe carrier to extend out of the openinas of the chamber to facilitatecontact of the osteogenic composition with the highly vascularizedtissue surrounding the fusion site. The carrier can also be provided inseveral strips sized to fit within the chamber. The strips can be placedone against another to fill the interior. As with the folded sheet, thestrips can be arranged within the spacer in several orientations.Preferably, the osteogenic material, whether provided in a sponge, asingle folded sheet or in several overlapping strips, has a lengthcorresponding to the length and width of the chamber.

[0118] The most preferred carrier is a biphasic calcium phosphateceramic. FIG. 49 shows a ceramic carrier 32 packed within a dowel 40.Hydroxyapatite/tricalcium phosphate ceramics are preferred because oftheir desirable bioactive properties and degradation rates in vivo. Thepreferred ratio of hydroxyapatite to tricalcium phosphate is betweenabout 0:100 and about 65:35. Any size or shape ceramic carrier whichwill fit into the chambers defined in the load bearing member arecontemplated. Ceramic blocks are commercially available from SofamorDanek Group, B. P. 4-62180 Rang-du-Fliers, France and Bioland, 132 Routed:Espagne, 31100 Toulouse, France. Of course, rectangular and othersuitable shapes are contemplated. The osteoinductive factor isintroduced into the carrier in any suitable manner. For example, thecarrier may be soaked in a solution containing the factor.

[0119] In a preferred embodiment, an osteogenic composition is providedto the pores of the load bearing member. The bone growth inducingcomposition can be introduced into the pores in any suitable manner. Forexample, the composition may be injected into the pores of the graft. Inother embodiments, the composition is dripped onto the graft or thegraft is soaked in a solution containing an effective amount of thecomposition to stimulate osteoinduction. In either case the pores areexposed to the composition for a period of time sufficient to allow theliquid to throughly soak the graft. The osteogenic factor, preferably aBMP, may be provided in freeze-dried form and reconstituted in apharmaceutically acceptable liquid or gel carrier such as sterile water,physiological saline or any other suitable carrier. The carrier may beany suitable medium capable of delivering the proteins to the spacer.Preferably the medium is supplemented with a buffer solution as is knownin the art. In one specific embodiment of the invention, rhBMP-2 issuspended or admixed in a carrier, such as water, saline, liquidcollagen or injectable BCP. The BMP solution can be dripped into thegraft or the graft can be immersed in a suitable quantity of the liquid.In a most preferred embodiment, BMP is applied to the pores of the graftand then lypholized or freeze-dried. The graft-BMP composition can thenbe frozen for storage and transport.

[0120] Advantageously, the intervertebral spacers of the presentinvention may not require internal fixation. The spacers are containedby the compressive forces of the surrounding ligaments and muscles, andthe disc annulus if it has not been completely removed. Temporaryexternal immobilization and support of the instrumented and adjacentvertebral levels, with a cervical collar, lumbar brace or the like, isgenerally recommended until adequate fusion is achieved.

[0121] Although the spacers and compositions of this invention make theuse of metal devices typically unnecessary, the invention may beadvantageously combined with such devices. The bone graft-osteogeniccompositions of the invention can be implanted within any of the variousprior art metal cages.

[0122] The following specific examples are provided for purposes ofillustrating the invention, and no limitations on the invention areintended thereby.

EXPERIMENTAL I: PREPARATION OF DEVICES EXAMPLE 1 Diaphysial CorticalBone Dowel

[0123] A consenting donor (i.e., donor card or other form of acceptanceto serve as a donor) was screened for a wide variety of communicablediseases and pathogens, including human immunodeficiency virus,cytomegalovirus, hepatitis B, hepatitis C and several other pathogens.These tests may be conducted by any of a number of means conventional inthe art, including but not limited to ELISA assays, PCR assays, orhemagglutination. Such testing follows the requirements of: (i) AmericanAssociation of Tissue Banks, Technical Manual for Tissue Banking,Technical Manual—Musculoskeletal Tissues, pages M19-M20; (ii) The Foodand Drug Administration, Interim Rule, Federal Register/Vol. 50, No.238/Tuesday, Dec. 14, 1993/Rules and Regulations/65517, D. InfectiousDisease Testing and Donor Screening, (iii) MMWR/Vol. 43/No. RR-8,Guidelines for Preventing Transmission of Human Immunodeficiency VirusThrough Transplantation of Human Tissue and Organs, pages 4-7; (iv)Florida Administrative weekly, Vol. 10, No. 34, Aug. 21, 1992,59A-1.001-014 59A-1.005(12)(c), F.A.C., (12)(a)-(h), 59A-1.005(15),F.A.C., (4)(a)-(8). In addition to a battery of standard biochemicalassays, the donor, or their next of kin, was interviewed to ascertainwhether the donor engaged in any of a number of high risk behaviors suchas having multiple sexual partners, suffering from hemophilia, engagingin intravenous drug use etc. After the donor was ascertained to beacceptable, the bones useful for obtention of the dowels were recoveredand cleaned.

[0124] A dowel was obtained as a transverse plug from the diaphysis of along bone using a diamond tipped cutting bit which was water cleaned andcooled. The bit was commercially available (Starlite, Inc) and had agenerally. circular nature and an internal vacant diameter between about10 mm to about 20 mm. The machine for obtention of endo- and corticaldowels consisted of a pneumatic driven miniature lathe which isfabricated from stainless steel and anodized aluminum. It has a springloaded carriage which travels parallel to the cutter. The carriage rideson two runners which are 1.0 inch stainless rods and has a traveldistance of approximately 8.0 inches. One runner has set pin holes onthe running rod which will stop the carriage from moving when the setpin is placed into the desired hole. The carriage is moveable from sideto side with a knob which has graduations in metric and in English. Thisallows the graft to be positioned. On this carriage is a vice whichclamps the graft and holds it in place while the dowel is being cut. Thevice has a cut out area in the jaws to allow clearance for the cutter.The lathe has a drive system which is a pneumatic motor with a valvecontroller which allows a desired RPM to be set.

[0125] First, the carriage is manually pulled back and locked in placewith a set pin. Second, the graft is loaded into the vice and is alignedwith the cutter. Third, the machine is started and the RPM is set, byusing a knob on the valve control. Fourth, the set pin, which allows thegraft to be loaded onto the cutter to cut the dowel. Once the cutter hascut all the way through the graft the carriage will stop on a set pin.Fifth, sterile water is used to eject dowel out of the cutter. It isfully autoclavable and has a stainless steel vice and/or clampingfixture to hold grafts for cutting dowels. The graft can be positionedto within 0.001′ of an inch which creates dowel uniformity during thecutting process.

[0126] The cutter used in conjunction with the above machine can producedowels ranging from 5 mm to 30 mm diameters and the sizes of the cuttersare 10.6 mm; 11.0 mm; 12.0 mm; 13.0 mm; 14.0 mm; 16.0 mm; and 18.0 mm.The composition of the cutters is stainless steel with a diamond powdercutting surface which produces a very smooth surface on the wall of thedowels. In addition, sterile water is used to cool and remove debrisfrom graft and/or dowel as the dowel is being cut (hydro infusion). Thewater travels down through the center of the cutter to irrigate as wellas clean the dowel under pressure. In addition, the water aides inejecting the dowel from the cutter.

[0127] The marrow was then removed from the medullary canal of the doweland the cavity cleaned to create of chamber. The final machined productmay be stored, frozen or freeze-dried and vacuum sealed for later use.

EXAMPLE 2 Threaded Dowels

[0128] A diaphysial cortical bone dowel is prepared as described above.The plug is then machined, preferably in a class 10 clean room, to thedimensions desired. The machining is preferably conducted on a lathesuch as a jeweler's lathe or machining tools may be specificallydesigned and adapted for this purpose. A hole is then drilled throughthe anterior wall of the dowel. The hole is then tapped to receive aitthreaded insertion tool.

EXAMPLE 3 Bone Dowel Soaked With rhBMP-2

[0129] A threaded dowel is obtained through the methods of Examples 1and 2.

[0130] A vial containing 4.0 mg of lyphilized rhBMP-2 (GeneticsInstitute) is constituted with 1 mL sterile water (Abbott Laboratories)for injection to obtain a 4.0 mg/mL solution as follows:

[0131] 1. Using a 3-cc syringe and 22 G needle, slowly inject 1.0 mLsterile water for injection into the vial containing lyphilized rhBMP-2.

[0132] 2. Gently swirl the vial until a clear solution is obtained. Donot shake.

[0133] The dilution scheme below is followed to obtain the appropriaterhBMP-2 concentration. This dilution provides sufficient volume for twodowels. The dilutions are performed as follows:

[0134] 1. Using a 5-cc syringe, transfer 4.0 mL of MFR 906 buffer(Genetics Institute) into a sterile vial.

[0135] 2. Using a 1-cc syringe, transfer 0.70 mL reconstituted rhBMP-2into the vial containing the buffer.

[0136] 3. Gently swirl to mix. DILUTION SCHEME INITIAL rhBMP-2 rhBMP-2MFR-842 FINAL rhBMP-2 CONCENTRATION VOLUME VOLUME CONCENTRATION (mg/mL)(mL) (mL) (mg/mL) 4.0 0.7 4.0 0.60

[0137] 1. Using a 3-cc syringe and 22 G needle, slowly drip 2.0 mL of0.60 mg/mL rhBMP-2 solution onto the Bone Dowel.

[0138] 2. Implant immediately.

EXAMPLE 4 Bone Dowel Packed With BMP-2/Collagen Composition

[0139] A threaded dowel is obtained through the methods of Examples 1and 2.

[0140] A vial containing 4.0 mg of lyphilized rhBMP-2 (GeneticsInstitute) is constituted with 1 mL sterile water (Abbott Laboratories)for injection to obtain a 4.0 mg/mL solution as follows:

[0141] 1. Using a 3-cc syringe and 22 G needle, slowly inject 1.0 mLsterile water for injection into the vial containing lyphilized rhBMP-2.

[0142] 2. Gently swirl the vial until a clear solution is obtained. Donot shake.

[0143] The dilution scheme below is followed to obtain the appropriaterhBMP-2 concentration. The dilutions are performed as follows:

[0144] 1. Using a 3-cc syringe, transfer 2.5 mL of MFR-842 buffer(Genetics Institute) into a sterile vial.

[0145] 2. Using a 1-cc syringe, transfer 0.30 mL of 4.0 mg/mLreconstituted rhBMP-2 into the vial containing the buffer.

[0146] 3. Gently swirl to mix. DILUTION SCHEME INITIAL rhBMP-2 rhBMP-2MFR-842 FINAL rhBMP-2 CONCENTRATION VOLUME VOLUME CONCENTRATION (mg/mL)(mL) (mL) (mg/mL) 4.0 0.3 2.5 0.43

[0147] The rhBMP-2 solution is applied to a Helistat sponge (GeneticsInstitute) as follows:

[0148] 1. Using sterile forceps and scissors, cut a 7.5 cm×2.0 cm stripof Helistat off of a 7.5×10 cm (3″×4″) sponge.

[0149] 2. Using a 1-cc syringe with a 22-G needle, slowly dripapproximately 0.8 mL of 0.43 mg/mL rhBMP-2 solution uniformly onto theHelistat sheet.

[0150] 3. Using sterile forceps, loosely pack the sponge into thechamber of the dowel.

[0151] 4. Using a 1-cc syringe with a 22-G needle, inject the remaining0.8 mL of 0.43 mg/mL rhBMP-2 into the sponge in the dowel through theopenings of the chamber.

[0152] 5. Implant immediately.

EXAMPLE 5 Bone Dowel Packed rhBMP-2/HA/TCP Composition

[0153] A threaded dowel is obtained through the methods of Examples 1and 2.

[0154] A vial containing 4.0 mg of lyphilized rhBMP-2 (GeneticsInstitute) is constituted with 1 mL sterile water (Abbott Laboratories)for injection to obtain a 4.0 mg/mL solution as follows:

[0155] 1. Using a 3-cc syringe and 22 G needle, slowly inject 1.0 mLsterile water for injection into the vial containing lyphilized rhBMP-2.

[0156] 2. Gently swirl the vial until a clear solution is obtained. Donot shake.

[0157] A cylindrical block of biphasic hydroxyapatite/tricalciumphosphate (Bioland) is wetted with a 0.4 mg/mL rhBMP-2 solution. TheBMP-ceramic block is packed into the chamber of the dowel and the dowelis then implanted.

EXAMPLE 6 Cortical Ring

[0158] A screened consenting donor is chosen as described in EXAMPLE 1as follows. A cortical ring is obtained as a cross-sectional slice ofthe diaphysis of a human long bone and then prepared using the methodsdescribed in Example 1. The ring is packed with an osteogeniccomposition as described in EXAMPLE 4 or 5.

EXAMPLE 7 Spacers

[0159] A screened consenting donor is chosen as described in EXAMPLE 1.A D-shaped cervical spacer is obtained as a cross-sectional slice of adiaphysis of a long bone and then prepared using the methods ofExample 1. The exterior surfaces of the walls are formed by machiningthe slice to a D-shape. The engaging surfaces of the spacer are providedwith knurlings by a standard milling machine. A hole is then drilledthrough the anterior wall of the spacer. The hole is then tapped toengage a threaded insertion tool. The chamber of the spacer is thenpacked with an osteogenic composition as described in EXAMPLE 4 or 5.

EXPERIMENTAL II: BIOMECHANICAL TESTING EXAMPLE 10 Static Testing OfThreaded Cortical Dowels Under Axial Loading

[0160] Static testing was performed to assure that the dowels were ableto withstand maximum physioloc loading, of at least 10,000 N, themaximum expected lumbar load. Eighteen (18) mm outer diameter, frozenthreaded cortical dowels 40 were obtained from the University of FloridaTissue Bank and thawed for testing with an axial test fixture 300. Four(4) samples of the threaded cortical dowel were inserted into twoprepared plastic (polyacetal polymer) blocks 301, 302 having matchinggeometry with the threaded cortical dowels 40 as shown in FIGS. 50-52.The plastic blocks 301, 302 were attached to metallic blocks 301, 302 toensure uniform loading across the dowel 40. A disc height H of 9 mm wasused for the testing. An axial load I was applied via a servohydraulictest machine to the blocks 301, 302, 303, 304 at a rate of 25 mm/min.until failure of the dowel 40. The load-displacement curves wererecorded.

[0161] Results:

[0162] The threaded dowels yielded at an average load of 24,733 N. Thecompressive strength of the threaded cortical dowels provides for asignificant safety factor compared to both typical and maximumphysiological spinal loading as shown in FIG. 53. These values rangefrom 1000 N when standing to 10,000 N for heavy lifting. The compressivestrength of threaded cortical dowels and cortical rings exceeds that ofmost available bone materials used for interbody fusion as shown in FIG.54. Overall, the threaded cortical dowels and cortical rings testeddemonstrated superior compressive strength compared to availableoptions, with the exception of the femoral ring allograft. Note that thetesting was for a single dowel. Clinically, most cases involve theplacement of dual, bilateral dowels. Therefore, the expected averagemaximum compressive load for 2 dowels would be 49,466 N, comparable tothe femoral ring allograft values. The threaded cortical dowels alsocompare favorably to artificial interbody implants as shown in FIG. 55.

EXAMPLE 11 Dynamic Testing Of Threaded Cortical Dowels Under AxialLoading

[0163] Dynamic testing determines the fatigue performance of the dowelunder cyclic loading. Cycles to failure are determined at various loadlevels. Resistance to fatigue is important to the performance of spinalimplants. The implant must be able to withstand cyclic in vivo loadinguntil fusion occurs. It is estimated that the average person makes 2million strides per year (1 million gait cycles) and 125,000 significantbends per year. Therefore, the typical dynamic testing run-out value of5 million cycles simulates approximately 2 years of cyclic loading priorto fusion and ultimate complete spinal motion segment stabilization.

[0164] The fixture 300 (FIGS. 50-52) described in Example 11 for theaxial static testing was used to apply dynamic alternating loads tovarious implants and dowels. Initial fatigue loads were determined basedon the maximum static load value. Initial fatigue loads were 75%, 50%and 25% of the ultimate strength value of 24,733 N. Additional datapoints were then generated to determine the five million cycle runoutvalue.

[0165] Results:

[0166] Based on the previously discussed physiologic loading values, anaverage every day loading value in expected to be a fraction of themaximum values and is estimated at approximately 3,200 N. This typicalloading value can then be used to assess the fatigue performance of thevarious interbody fusion alternatives. For the threaded cortical dowel,runout was achieved at a level of 30% of the maximum static load. Thatis, a minimum of 2 samples reached 5 million cycles at an applied loadof 7,420 N as shown in FIG. 56. This value is well above the averageloading value of 3200 N. EXAMPLE 12

Static And Dynamic Testing Of Threaded Cortical Dowels Under BendingLoads

[0167] While compressive testing provided valuable comparativeinformation regarding the dynamic and static performance of the dowels,it is a simplification of the loading seen by the dowels in the clinicalsettings. In order to better simulate the loading seen clinically, aspecial flexion-extension or multi-axial cyclic test fixture 310 wasdeveloped (FIGS. 57 and 58). Dowels were tested in both static anddynamic loading situations. The specially designed fixture appliedcomplex, multi-axial loading to the dowels.

[0168] The dowels were placed into pre-tapped plastic (polyacetalpolymer) blocks 311, 312. The plastic blocks 311, 312 are affixed torecessed pockets 313, 314 in the upper 315 and lower 316 plates of themetal test fixture 318. Vertical loads L are applied to generate theflexion-extension bending moments. Cyclic compressive loads are applied,and a bending moment is generated by the 7.6 cm loading arm.

[0169] Two dowels were subject to a static load to failure in the testfixture. The maximum load value was then used to determine dynamicloading values. For the fatigue testing, fully reversed loading wasapplied, simulating flexion-extension cycles. Cyclic testing was carriedout at values of 40%, 30% and 20% of the maximum load value and the 5million cycle runout value was determined.

[0170] Results:

[0171] The average static load to failure value for the threadedcortical dowel was found to be 1,545 N. Given the 7.6 cm moment arm,this translates into a value of 138 N-m maximum bending load. The 5million cycle runout value was approximately 450 N. Again, given the 7.6cm moment arm, this translates into a value of 40.5 N-m bending load. Itis reported that the failure load of a lumbar motion segment in bendingis 33 N-m on average. The maximum static load value is over 4 timeshigher than this value, and the dynamic, multi-axial runout value isabove this maximum bending load value.

EXAMPLE 13 Insertion Torque Testing Of Threaded Cortical Dowels

[0172] Benchtop testing was performed to study the insertion torquerequired to insert the dowels and to compare these values with that ofthreaded interbody fusion devices. Two (2) lumbar calf spines were usedfor the insertion torque testing. Due to size constraints, an 18 mmthreaded cortical dowel was inserted into the lowest two lumbar levelsof each spine. The disc spaces were dilated and the space was reamed andthen tapped. A specially modified driver was used to place the dowelsand measure the insertion torque.

[0173] Results:

[0174] No damage was noted to any of the dowels upon examination afterinsertion. The average insertion torque value was found to be 0.78 N-m.The threaded cortical dowel compared favorably to known values for metalthreaded fusion devices as shown in FIG. 59.

Summary Of Threaded Cortical Dowel Testing

[0175] The biomechanical testing demonstrates that the threaded corticaldowels are well suited for interbody fusion applications. The testinformation is summarized as follows:

[0176] 1. The static strength of threaded cortical dowels provides for asubstantial safety factor over maximum physiologic load levels. Thedowels are stronger than alternative bone dowel constructs. Theirstrength exceeds that of the Brantigan composite PLIF cage and the RayTFC device and is comparable in strength to the SpineTech BAK.

[0177] 2. The fatigue strength of the threaded cortical dowels exceedsthat of conventional Crock-type bone dowels and provides for asubstantial safety factor over typical, daily living load levels. Thefatigue strength of the dowels exceeds that of the Ray TFC device and iscomparable to the SpineTech BAK device.

[0178] 3. The dowels are able to resist maximum bending loads, providingfor a substantial safety factor in satic loading and demonstrating 5million cycle runout at a value above the maximum expected bendingloads.

[0179] 4. The torque recquired to insert the devices is comparable withthat seen with threaded fusion cages. No damage to the threads or thedowel drive attachment were detected when inserting and revising thedowels.

[0180] Overall, the threaded cortical dowels possess the requiredbiomechanical properties to facilitate interbody fusion in the lumbarspine. Their physical strength well exceeds the expected physiologicalloading and is superior to other bone graft alternatives. The dowelsoutperform or are comparable to all currently available fusion cagealternatives.

EXAMPLE 14 Evaluation of rhBMP-2 as a Bone Graft Enhancing Agent

[0181] The purpose of this study was to determine the effect of usingBMP to augment allograft to fill a gap surrounding a porous coatedimplant. A non-weight bearing canine model was used. Raw MaterialsAMOUNT MATERIAL SOURCE/LOT # COMMENTS SUPPLIED rhBMP-2 GeneticsInstitute 4 mg/mL rhBMP-2 in 4 vials at Lot# 0214C01 5 mM sodium 4mg/vial lyo. TQ Fill glutamate, 2.5% from MFR842 glycine, 0.5% buffersucrose, 0.01% Tween 80, pH 4.5 MFR842 Genetics Institute 5 mM sodium 4vials at Buffer Lot # 26256 glutamate. 2.5% 5 mL/vial glycine, 0.5%sucrose, 0.01% Tween 80, pH 4.5 Irradiated Fresh, Donor CaninesIrradiated 2.5 Mrads Approximately Frozen Canine (24-26 KG's) 10-15 mLsAllograft Vitallium Porous Howmedica 5.4 mm diameter N/A Coated PlugsTeflon Washers Howmedica I.D. 6.4 mm, N/A O.D. 10.4 mm Autogenic bloodN/A N/A N/A Sterile Water for Injection Abbott Labs Lot# 90-544-DK WFIUSP Grace 4 vials at 10 mL/vial

[0182] Composition and Graft Preparation 1. Allograft Preparation a.Draw 1 mL canine blood. b. Add 0.700 mL canine blook to a sterile 1.5 mLeppendorf tube. c. Mark level on this tube. d. Mark level on a secondtube and discard the tube containing blood. e. Mark level on threeadditional tubes. f. Add allograft to level marked on tubes. 2.Allograft/Blood/rhBMP-2 Compositions a. Reconstitute the rhBMP-2 using 1mL, room temperature, sterile water for injection (WFI). Inject the WFIinto a vial of rhBMP-2, along the inside surface of the vial. Gentlyswirl the vial 3-4 times. The final concentration is 4 mg/mL. b. Draw1.0 mL canine blood and place in a sterile eppendorf tube. c. Draw 0.550mL of blood from the tube and place into a second eppendorf tube. d. Add0.050 mL blood of the reconstituted rhBMP-2 solution to the 0.550 mLblood and mix gently with a siliconized pipet tip. e. Add 0.300 mL ofthe blood/rhBMP-2 mixture to the eppendorf tube containing theallograft. f. Stir the material gently with a sterile spatula until wellmixed. g. Let clot at room temperature for 1 hour. 3.Allograft/Blood/MFR842 Composition a. Draw 1.0 mL canine blood and placein a sterile eppendorf tube. b. Draw 0.550 mL of blood from the tube andplace into a second eppendorf tube. c. Add 0.050 mL of the MFR842 Bufferto the 0.550 mL blood and mix gently with a siliconized pipet tip. d.Add 0.300 mL of the blood/MFR842 mixture to the eppendorf tubecontaining the allograft. e. Stir the material gently with a sterilespatula until well mixed. f. Let clot at room temperature for 1 hour.

[0183] Surgery

[0184] Graft compositions were placed across each femoral condyle with a2 mm cap maintained throughout the cancellous region of the condyle. Thecomposition on the left included fresh-frozen allograft and thecomposition on the right included fresh-frozen allograft plus rhBMP-2 asshown in the table below. Scheme Treated: Control: Bone + Canine ID BoneGraft Only rhBMP-2 Time 94-975 Right leg Left leg 14 days 94-973 Rightlegg Left leg 14 days 94-913 Right leg Left leg 28 days 94-914 Right legLeft leg 28 days

[0185] The implanted compositions were evaluated radiographically andeffectiveness was tested using biomechanical shear testing or push-outstrength. Five mm thick sections were obtained for the push-out tests bymaking a cut 5 mm from the lateral end of the metal implant and a secondcut 5 mm from the first this cut. This resulted in three sections perbone specimen with the exception of one specimen which yielded foursections due to repositioning of the bone block. The biomechanical testswere completed using a computer-linked servohaudraulic materials tester.

[0186] Results

[0187] The surgeries were uneventful. The dogs were all full weightbearing within 3 days (2±1.15).

[0188] Presurgical radiographs of the distal femora from all animalsrevealed normal, mature bone structure with no radiographic pathology.Post-operative and terminal evaluation of the implantation sites wereperformed to assure the correctness of implant placement and to documentchanges around the implant site. No fractures or other surgicalcomplications were recognized on the radiographic images.

[0189] Push-out (compression) was achieved using a rate of 0.5 mm/sec.All specimens appeared to fail at the graft-metal interface. All of thetwo week specimens could be pushed our easily by finger-touch or bygravity alone. Push out testing does not appear to be adequate parameterfor comparison of the treated vs. un-treated groups at this time period.Specimens from the treated animals at the 4 week time period wereclearly superior to the untreated specimens as shown in the table below.Load to Failure Values(N) Time After Left Right Canine ID SurgeryGraft + BMP Graft Alone 975 2 weeks 8.71 24.43 973 2 weeks 17.45 12.22913 4 weeks 82.88 41.88 914 4 weeks 76.78 13.96

[0190] Push-out strength for the BMP-treated specimens was superior tothe graft alone specimens after four weeks, suggesting a BMP enhancementof mechanical strength. The failure at the graft-metal interfaceindicates a weak bond between the metal and bone four weekspostoperatively.

Conclusion

[0191] The combination of BMP with a bone graft provides superiorresults. Quicker fusion rates provide enhanced mechanical strengthsooner. Bone is an excellent protein carrier which provides controlledrelease of BMP to the fusion site. When the bone graft is a threadedcortical dowel, the biomechanical superiority of the load bearing dowelis superbly combined with the enhanced fusion rates of the BMP-bonecombination.

[0192] While the invention has been illustrated and described in detailin the drawings and foregoing description, the same is to be consideredas illustrative and not restrictive in character, it being understoodthat only the preferred embodiments have been shown and described andthat all changes and modifications that come within the spirit of theinvention are desired to be protected.

What is claimed:
 1. A spinal spacer comprising a load bearing memberhaving a wall sized for engagement within a space between adjacentvertebrae to maintain the space, said load bearing member including abone graft impregnated with an effective amount of an osteogeniccomposition to stimulate osteoinduction, said osteogenic compositionincluding a substantially pure osteogenic factor in a pharmaceuticallyacceptable carrier.
 2. The spacer of claim 1 wherein said osteogenicfactor is a purified bone morphogenic protein isolated from bone.
 3. Thespacer of claim 1 wherein said osteogenic factor protein is arecombinant human protein.
 4. The spacer of claim 3 wherein said bonemorphogenic protein is selected from the group consisting of BMP-1,BMP-2, BMP-3, BMP-4, BMP-5, BMP-6, BMP-7, BMP-8, BMP-9, BMP-10, BMP-11,BMP-12, BMP-13, a mixture thereof and a heterodimer thereof.
 5. Thespacer of claim 4 wherein said bone morphogenic protein is rhBMP-2,rhBMP-7 or a mixture or heterodimer thereof.
 6. The spacer of claim 1wherein said carrier is physiological saline.
 7. The spacer of claim 1wherein said carrier is buffered sterile water.
 8. The spacer of claim 1wherein said member is a cylindrical bone dowel having a diameter largerthan the height of the space between the adjacent vertebrae.
 9. Thespacer of claim 8 wherein said bone member defines a chamber and saidbone graft is a bone dowel obtained from the diaphysis of a long bonehaving a medullary canal, said chamber including a portion of saidcanal.
 10. The spacer of claim 9 further comprising an effective amountof a second osteogenic composition to stimulate osteoinduction, saidsecond composition packed within said chamber.
 11. The spacer of claim10 wherein said second composition has a length which is greater than alength of said chamber and said second composition is disposed withinsaid chamber to contact the endplates of adjacent vertebrae when thegraft is implanted between the vertebrae.
 12. The spacer of claim 11wherein said second osteogenic composition is selected from the groupconsisting of autograft, allograft, demineralized bone, calciumphosphate ceramics, and an osteoinductive factor disposed within apharmaceutically acceptable matrix
 13. The spacer of claim 1 whereinsaid member includes an anterior wall and said anterior wall defines atool engaging hole for receiving an implanting tool.
 14. The spacer ofclaim 1 wherein said member includes at least two opposite bone engagingsurfaces for contacting a corresponding one of the adjacent vertebraewhen the spacer is implanted therebetween, at least one of said engagingsurfaces defining surface roughenings.
 21. The spacer of claim 18wherein said threads define an angle between leading and trailing flanksof adjacent ones of said teeth, said angle between about 50 degrees and70 degrees.
 22. The spacer of claim 18 wherein each said tooth has aheight between about 0.030 inches and about 0.045 inches.
 23. The spacerof claim 18 wherein said dowel includes a tool engaging portion defininga tool engaging hole for receiving an implanting tool.
 24. The spacer ofclaim 23 wherein said tool engaging hole is threaded to receive athreaded implanting tool.
 25. A spinal spacer comprising a load bearingmember having a wall sized for engagement within a space betweenadjacent vertebrae to maintain the space, said load bearing memberdefining a chamber and including a bone graft obtained from thediaphysis of a long bone having a medullary canal said chamber includinga portion of the canal, and an effective amount of an osteogeniccomposition to stimulate osteoinduction, said composition including asubstantially pure osteogenic factor in a pharmaceutically acceptablematrix and packed within said chamber.
 26. The spacer of claim 25wherein said composition has a length which is greater than a length ofsaid chamber and said composition is disposed within said chamber tocontact the endplates of adjacent vertebrae when the spacer is implantedbetween the vertebrae.
 27. The spacer of claim 26 wherein saidosteogenic factor is a purified bone morphogenic protein isolated frombone.
 28. The spacer of claim 26 wherein said osteogenic factor is arecombinant human bone morphogenic protein.
 29. The spacer of claim 28wherein said osteoinductive factor is a bone morphogenic protein andsaid protein is selected from the group consisting of BMP-1, BMP-2,BMP-3, BMP-4, BMP-5, BMP-6, BMP-7, BMP-8, BMP-9, BMP-10, BMP-11, BMP-12,BMP-13, a mixture thereof and a heterodimer thereof.
 30. The spacer ofclaim 29 wherein said bone morphogenic protein is rhBMP-2, rhBMP-7 or amixture or heterodimer thereof.
 31. The spacer of claim 30 wherein saidmatrix is selected from the group consisting of calcium sulphates,polylactic acids, polyanhydrides, collagen, calcium phosphates andpolymeric acrylic esters.
 32. The spacer of claim 31 wherein said matrixincludes a bioceramic.
 33. The spacer of claim 32 wherein saidbioceramic is a calcium phosphate ceramic.
 34. The spacer of claim 33wherein said ceramic is a biphasic calcium phosphate ceramic, includinghydroxyapatite and tricalcium phosphate.
 35. The spacer of claim 34wherein the ratio of hydroxyapatite to tricalcium phosphate is betweenabout 0:100 and about 65:35.
 36. The spacer of claim 25 wherein saidbone dowel includes an outer surface and said outer surface defines atool engaging hole for receiving an implanting tool.
 37. The spacer ofclaim 25 wherein said member is a bone dowel having an outer surfacedefining threads, said threads being uniformly machined threads, saidthreads including teeth each having a crest between a leading flank andan opposite trailing flank.
 38. The spacer of claim 37 wherein saidcrest of each said tooth is flat, having a width of between about 0.020inches and about 0.030 inches.
 39. The spacer of claim 38 wherein saidthreads define an angle between leading and trailing flanks of adjacentones of said teeth, said angle between about 50 degrees and 70 degrees.40. The spacer of claim 38 wherein each said tooth has a height betweenabout 0.030 inches and about 0.045 inches.
 41. The spacer of claim 37wherein said dowel includes a tool engaging portion defining a toolengaging hole for receiving an implanting tool.
 42. The spacer of claim41 wherein said tool engaging hole is threaded to receive a threadedimplanting tool.
 43. The spacer of claim 25 wherein said graft is acortical ring obtained by a cross-sectional slice of the diaphysis, saidring including superior and inferior surfaces and said osteogenic factoris a bone morphogenic protein.
 44. The spacer of claim 43 wherein saidprotein is selected from the group consisting of BMP-1, BMP-2, BMP-3,BMP-4, BMP-5, BMP-6, BMP-7, BMP-8, BMP-9, BMP-10, BMP-11, BMP-12,BMP-13, a mixture thereof and a heterodimer thereof.
 45. The spacer ofclaim 44 wherein said bone morphogenic protein is rhBMP-2, rhBMP-7 or amixture or heterodimer thereof.
 46. The spacer of claim 43 wherein saidmatrix is selected from the group consisting of calcium sulphates,polylactic acids, polyanhydrides, collagen, calcium phosphates andpolymeric acrylic esters.
 47. The spacer of claim 46 wherein said matrixincludes a biphasic calcium phosphate ceramic, including hydroxyapatiteand tricalciun phosphate.
 48. The spacer of claim 43 wherein said ringincludes an outer surface adjacent and between said superior andinferior surfaces and said outer surface defines a tool engaging holefor receiving an implanting tool.
 49. The spacer of claim 43 wherein atleast one of said superior and inferior surfaces are roughened.
 50. Thespacer of claim 43 wherein at least one of said superior and inferiorsurfaces includes teeth.
 51. The spacer of claim 43 wherein at least oneof said superior and inferior surfaces defines a waffle pattern.
 52. Thespacer of claim 37 wherein said load bearing member has a compressivestrength of at least 10,000 N.
 53. The spacer of claim 52 wherein saidload bearing member has a compressive strength of at least 20,000 N. 54.The spacer of claim 37 wherein said load bearing member has a fatiguestrength of at least 3200 N at five million cycles.
 55. The spacer ofclaim 54 wherein said load bearing member has a fatigue strength of atleast 7000 N at five million cycles.
 56. A hollow spinal spacer forengagement between vertebrae, comprising: an anterior wall having aconvexly curved anterior surface and opposite ends; a posterior wallhaving a flat posterior surface and opposite ends; two lateral walls,each integrally connected between said opposite ends of said anteriorand posterior walls to define a chamber; and said walls comprised ofbone and further defining; a superior face defining a first opening,said opening in communication with said chamber, said superior facehaving a superior engaging surface; and an opposite inferior facedefining a second opening, said second opening in communication withsaid chamber, said inferior face having an inferior engaging surface.57. The spacer of claim 56 wherein said bone is cortical bone obtainedfrom the diaphysis of a long bone having a medullary canal, said chamberincluding a portion of the medullary canal.
 58. The spacer of claim 56,further comprising an effective amount of an osteogenic composition tostimulate osteogenesis, said composition disposed within said chamber.59. The spacer of claim 56 wherein said osteogenic composition includesa material selected from the group consisting of autograft, allograft, abioceramic and a substantially pure osteogenic factor in apharmaceutically acceptable matrix.
 60. The spacer of claim 59 whereinsaid bioceramic is a biphasic calcium phosphate ceramic.
 61. The spacerof claim 59 wherein said factor includes a bone morphogenic proteinselected from the group consisting of BMP-1, BMP-2, BMP-3, BMP-4, BMP-5,BMP-6, BMP-7, BMP-8, BMP-9, BMP-10, BMP-11, BMP-12 and BMP-13, a mixturethereof and a heterodimer thereof.
 62. The spacer of claim 61 whereinsaid matrix is selected from the group consisting of calcium sulphates,polylactic acids, polyanhydrides, collagen, calcium phosphates andpolymeric acrylic esters.
 63. The spacer of claim 56 wherein saidanterior wall defines a tool engaging hole for receiving an implantingtool.
 64. The spacer of claim 63 wherein said tool engaging hole isthreaded for receiving a threaded implanting tool.
 65. The spacer ofclaim 56 wherein at least one of said engaging surfaces are roughened.66. The spacer of claim 56 wherein at least one of said engagingsurfaces includes teeth.
 67. The spacer of claim 56 wherein at least oneof said engaging surfaces defines a waffle pattern.
 68. The spacer ofclaim 56 further comprising a blade on at least one of said engagingsurfaces.
 69. The spacer of claim 1 wherein said graft is porous andsaid composition is contained within said pores.
 70. The spacer of claim1 wherein said wall defines a bone growth thru-hole therethrough, saidthru-hole sized to receive mesenchymal cells.
 71. The spacer of claim 25wherein said wall defines a bone growth thru-hole therethrough, saidthru-hole communicating with said chamber and sized to receivemesenchymal cells.
 72. The spacer of claim 56 wherein said wall definesa bone growth thru-hole therethrough, said thru-hole communicating withsaid chamber and sized to receive mesenchymal cells.